In the steps of forming a core substrate, an insulating layer or the like of a multilayer wiring board to be used in electronic equipment or the like, conventionally, there has been used a prepreg in which a glass fiber fabric or a polymer nonwoven fabric is impregnated with a thermosetting resin and is half cured. The prepreg is thermally pressed together with copper foils provided on both surfaces, for example, so that a double-sided copper foil laminated plate can be obtained, and a wiring pattern is formed on the copper foils and can be thus used as a double-sided wiring board (including a core substrate) for manufacturing a multilayer wiring board.
In recent years, the multilayer wiring board described above has a finer wiring pattern because of the high integration of a wiring, and furthermore, a multilayer structure is achieved and each layer is thinned. As the prepreg described above, therefore, there has been proposed a prepreg using, as a reinforcing phase, a polymer nonwoven fabric in which layers can be thinned and the laser via processing can be carried out more easily.
In a prepreg using a polymeric nonwoven fabric as a reinforcing phase, however, a reduction in the thickness of a layer is limited for reasons of manufacture. Moreover, the irregularities of a fiber are easily generated on a surface and a flat insulating layer is formed with difficulty. For this reason, in a multilayer wiring board in which each layer has a thickness reduced, particularly, there has been employed a method in which a thermosetting resin is applied in place of the lamination of the prepreg or a thermosetting resin sheet is provided to form an insulating layer. In these methods, however, the reinforcing phase is not present. Therefore, it is hard to control a gap for forming the insulating layer. Thus, such a method is not advantageous in respect of mass production.
There has also been known a prepreg using a porous film comprising aromatic polyamide in place of the polymeric nonwoven fabric (Japanese Laid-Open Patent Publication No. 9-324060). Such a prepreg is usually used for manufacturing a double-sided copper foil laminated plate having a copper foil laminated and integrated on both surfaces.
Therefore, it is an object of the present invention to provide a method of manufacturing a multilayer wiring board which is advantage to mass production because gap control for forming an insulating layer is carried out easily, and furthermore, can provide thinner layers of the whole board and is advantageous to the flattening of the surface of the board, and a multilayer wiring board which can be obtained by the manufacturing method.